This invention relates to an apparatus for finishing lenses. More specifically, this invention relates to an apparatus for polishing or fining spherical or toric surfaces of ophthalmic lenses. In ophthalmic lens finishing, the term "polish" or "fine" are terms of art indicating a degree of finish achieved. Since the subject apparatus is used for both polishing and fining the terms will be used interchangeably.
In the manufacture and finishing of ophthalmic lenses, lens blanks are first formed from glass or a plastic composition such as polymethylmethacrylate and a convex surface of the lens is mounted upon a retaining member known as a lens block. The lens and block are then accurately mounted upon a grinding apparatus wherein either a spherical surface or a toroidal surface of compound prescriptive value is rough-ground into a concave portion of the lens. (In toroidal lens a first principle meridian of the lens typically has a different dimension than a second principle meridian normal to the first.) Following the initial grinding operation, an ophthalmic lens is fined and then polished to a final prescriptive value. Left and right lenses are then mounted upon an edge grinding machine to cut the outer peripheral shape required to be compatible with an ultimate wearer's eyeglass frame.
The subject invention is directed to a polisher-finer apparatus and comprises an improvement over a Stith U.S. Pat. No. 3,732,647 of common assignment with the subject application. The Stith patent discloses a polisher-finer wherein lenses are finished by being biased into engagement with a lapping tool having a spherical or toric surface of a final desired prescription. The lapping tool is driven in an orbital, break-up motion relative to the lens to prevent ridges, grooves, and/or other aberrations from forming in the lens surface which might occur if regular or uniform motion devices were utilized. In addition to orbital break-up motion of the lapping tool, the Stith patent discloses moving the lens in a transverse motion from side-to-side.
Another advantageous form of polisher-finer apparatus is disclosed in a Hill et al. U.S. Pat. No. 4,320,599, again assigned to the assignee of the subject application. In the Hill et al. patent first and second assemblies are provided for carrying a lapping tool and lens, respectively, imparting an orbital break-up motion during a fining and polishing operation. The amplitude of orbital motion is variable in the Hill et al. structure by application of a novel cam assembly to adjust the degree of orbital break-up motion of the lens mounting and/or lapping tool.
In at least one other system, a lens polishing apparatus is disclosed wherein a lapping tool is driven through a gimbal assembly while a lens to be polished is mounted upon a unit which provides linear transverse motion and simultaneous front-to-rear motion during a polishing operation. Such linear motion, however, is operated by a two-position cam operated fluid (air) switch. Such actuation tends to produce a saw-tooth aberration on the lens surface to a degree which is not acceptable in many applications.
Although polisher-finer systems of the type previously described have been widely utilized, room for significant improvement remains. In this regard it would be desirable to decrease the speed and amplitude of motion of a lens lapping tool for enhanced control, while concomitantly maintaining the feet-per-minute of relative motion between a lens and tool to facilitate rapid polishing and fining. It would also be desirable to provide a system for achieving a novel motion to a lens in an X-Y plane which would eliminate any tendency for the creation of a saw-tooth aberrations on the lens. If this could be achieved the rate of finishing of an ophthalmic lens could be increased without sacrificing any of the system finishing quality.